Bob learned that his username and password for a popular game has been compromised. He contacts the company and resets all the information. The company suggests he use two-factor authentication; which

A fingerprint scanner represents the 'something you are' factor (biometric), while a username and password represent the 'something you know' factor. Combining these two distinct factor categories satisfies the definition of two-factor authentication. This is a classic MFA implementation pairing knowledge-based and biometric credentials.

A username and a stronger password are both 'something you know' credentials - this is single-factor authentication regardless of password strength.

A new username and password still represent only one factor category ('something you know') and does not constitute 2FA.

Using only a fingerprint scanner is single-factor authentication ('something you are') - removing the password eliminates the second factor rather than adding one.